DB9 electrical wiring

[flyboy1]

I am a very happy owner of a DB9 which has had some intermittent electrical faults since I have owned it, some fixed under warrantee others so occasional could not cause fault or find reason but still love the car.

Last night I arrived home car behaving with no problems, got out to unlock garage (engine running) and internal lights came on as normal. Got back in to put car away and no internal lights? Checked today and fuse 47 blown. This is not first time, it happened once before. Replaced fuse and it blew immediately. Checked with meter and found load side shorted to earth. Removed all internal lamps and checked wires for shorts nothing found. Removed fuse 17 in boot not blown but still short to earth. Removed relay 6 in boot still short to earth. Disconnected connectors to seat switch pack. Still short.

Removed connector C6 from central electronic module so harness is now isolated as far as I can determine from the circuit diagrams and checking pin 7 (orange wire) it is shorted to earth so fault is in harness somewhere. The manual says wires split at splice number SPL19-VILR/CA. Where is this located please as it looks like only way to track fault is hard way of peeling back insulation and checking each wire in turn?

This is likely to be a slow hard to track fault and as I am a qualified robotics Development Engineer do not want to spend a fortune with dealer to do what I am probably better qualified to do, though not sure how to replace a cable if find it is somewhere along a run. A picture of the cable harness would also help when fault found if a new cable is required.

So to summarise my request.

Where is splice SPL19-VILR/CA located?
Does any one have a schematic of the cable runs?
Can anyone confirm Fuse F47 only supplies the 6 internal lamps, the boot lamp relay (and 2 lamps via fuse F17) and the two 3 way connectors either side of the transmission tunnel to the Seat packs?

Any advice most gratefully received.

[dhallworth]

I'm not sure about the questions you've asked, however after reading your description, I can't help but wonder if it could be an issue with the door wiring loom. Could it be shorting on the A pillar or on the door?

If it only happened after you got out to open the garage door, could the opening/closing of the car door be what's triggered it?

I might be wrong and I'm sure there'll be others more qualified to answer your question then I am along shortly.

David.

[agaton12]

>Where is splice SPL19-VILR/CA located?
Schematic says CA=cabin. Not very helpful.
>Does any one have a schematic of the cable runs?
I only have one for the Vantage, but that is useless for fault tracing.
>Can anyone confirm Fuse F47 only......
According to my schematic yes, but we are probably looking at the same one.

I have only two ideas:
- Check for damage to the loom by the brake pedal, since it seems to have happened when you got out of the car.
- Do you have a low range ohm-meter.Could a check of resistance values to ground from C6 and from each endpoint give a clue to where the short might be?

[flyboy1]

Dear All, thanks for the replies. Sadly Astons are not simple like old days of wire from switch in door feeding lamps, the switches now feed into the car processors and it then decides which relay to turn on and Mosfet (to give soft start/dim) which in this instance originates from the central electronic module under foot well floor. I spent an interesting 8 hrs gradually pulling interior of car apart and checking for fault with test gear tracing where fuse 47 feeds. It actually goes to the splice mentioned which is somewhere in the loom (around front of car foot well loom is over inch in diameter) and starts as an orange wire as per manual and splits 10 ways somewhere which is the problem I face now.

Just to summarise where I am at. I identified and disconnected where each wire feeds e.g. internal lamp holders, relay in boot, seat switch modules, glove box switch LED, and when all disconnected there is a definite short to earth. What is annoying and bad practice is to embed splices into looms. Always a source of potential fault and especially so when central electronic module has spare connector slots and unused fuses so could have easily split it at the module making tracing fault much easier BUT probably still a pig to fix and run a new lead once I can find the splice. Any advice where splice is much appreciated and will then have to work out how to get access to the in most instances hidden loom.

Whilst checking I did find several places where cables were rubbing on the sharp cropped edged of metal components, all now re-positioned and extra insulated but sadly not the source of problem this time.

[agaton12]

Hi.
I still have no idea where the splice is located,but I still believe a resistanse check would indicate a possible short location.
Anyway, since there is a short to ground and you could not find any external damage, and if we further assume that there are not that many ground wires inside the loom to create a short, a likely candidate would be the seat switchpack parts of the loom, which do have ground wires included.

[flyboy1]

Thanks but you do not understand the Aston crazy wiring. Would be very simple to find the fault is a wire went from A-B another A-C, another A-D etc. Disconnect all wires from A and check which one has the fault. Simple IF I could find point A. Aston have a single fuse and a wire from it to point A where ever that is. So checking wire at fuse and get short to ground, probably part of chassis or mounting plates cutting through harness as have found several plates where the edges are sharp and wires rubbing (edges removed, taped and wires taped just in case in future) but no idea where the orange wire from fuse splits and hence which of the many cable bundles to track as orange wires are used for many other circuits. I have removed plugs and all lamps from the C, D etc ends of harness to make sure what they connect to is not the problem and putting meter on each end shows as expected short to earth so fault has not cut through a wire but has shorted it to chassis. Why they do not bring the many splices to a terminal strip or connector on a fuse box or even use separate fuses for each wire when there are plenty of spare fuse locations I do not know nor do I understand the idea of network systems with I/O and still running bundles of wired from front to back of car when should use local nodes. If I find where splice is will let you all know

[agaton12]

When I say 'low-range' I mean sufficiently low so you can find out the resistance to ground including the wire. If you check from all endpoints, the one with the lowest resistance will be the part where your short is located (assuming equal wire gauge and suitable ground point). You may even be able to guesstimate the distance to the short. To avoid false readings compare the values you get with the values between endpoints. The method assumes that the resistance of the short is less than the wire resistance. A modern can-bus system may be convoluted, but ohm's law still applies so long as it's not fiber optics.

[flyboy1]

Thanks thought about it early on and can measure down to micro ohms but all the wires are different lengths going to different places and then there is the length of chassis and the resistance of the aluminium to the fault so a pig to work out and cannot make sense of resistance readings. Even thought about trying RF and oscilloscope to try and see if could work out the resonant length of the wire from each component e.g. lamp holder to earth to see if it was anything like expected but doubt that will work as, as with the resistance option, expect fault is not too far into loom from fuse box. Just hope factory eventually will reply with location of the splice and picture of the harness routing.

[flyboy1]

Whoopppeee. Fixed it. Had resigned myself to re-wiring the 10 cables from the interior lighting fuse as cannot find he splice and likely to be inaccessible in harness so removed boot trim, rear seats, side panels, door sills, carpets, glove box and could see no sign of damage to the looms leading to the lamps etc. so then set about removing roof lamps mounts and front roof trim and when removing the passenger sun visor found one of the orange wires that feeds one of the roof lights had been trapped under the outer bearing mount and had shorted to the magnesium alloy roof frame. Bit of tape routing it correctly and all is fine. Cleaned up a load of glass shards from rear seat and boot where a rear screen from previous owner had shattered and had a good look at structure not normally visible. Impressed with quality of build and design.